🚀 go-pugleaf

In my listing of some 'reservations' about the instructional value of the
egg-drop contest, I neglected to even mention the biggest one:

Eggs vary considerably in strength of shell, thickness of shell, etc, and
often have weak regions of the shell. All of these contribute to a
variability of results which would confound any quantitative analysis of
the results (unless you sacrificed dozens of eggs and did a statistical
analysis). How does one select 'standard' eggs for this? :-) Of course:
obtain a standard hen.

Someone commented that this exercise has value because it gets students to
tinker, fiddle, and brainstorm an idea. I agree. These are valuable
hands-on skills which should be incorporated into education (preferably
at an early age), where appropriate. Let's be honest and admit that
that's what exercises like this are all about, and not claim that they
will teach, reinforce, or demonstrate physics principles in a clear-cut
way. The best student activities do both.

Ask the students afterwards to write an essay: What physics principles of
this course did this exercise use, demonstrate or teach?  What reliable
conclusions can we draw from the experience?

We teachers should ask ourselves what outcomes to expect from particular
exercises or demonstrations, and if we can't think of any which are part
of the course objectives we ought to ask whether class time could be spent
more productively on something else. One example which comes to mind is
the smoke-ring vortex generator. It's a flashy and popular demo, but what
physics can we squeeze from it? Are we prepared to discuss smoke vortices,
with all their messy mathematics? I think not. Can we even cite one
physics principle (important to the elementary course) which the demo
illustrates or teaches? No. Are we teachers prepared to give authoritative
and physically correct answers to questions students can easily ask (and
should ask), such as "Why does the smoke ring move through still air so
fast?" (Try to toss the box of smoke that fast), "Why is it so stable?",
"Are there other stable shapes possible?", "What would happen if the hole
in the box were not round, but square, or triangular, or ring-shaped?":
"What would happen if two smoke rings collided? Could they link? Might
they form a stable grouping of rings?", "Why does the smoke rotate within
the ring in the way it does, and not some other way?"; "Can you cite
literature references for the motivated student?". A colleague remarked "I
wouldn't expect even an *advanced* college physics class to deal with this
in a meaningful way!"

     Historical trivia: Martin Gardner's _New Ambidexterous Universe_ has a
     section about how turn-of-the-century physicists tried to model
     atomic particles and even atoms and molecules as vortex rings in
     the luminiferous ether. Huge vortex cannons were once used to shoot
     smoke rings into the sky in Austria, to protect vineyards from
     hailstorms. Of course it was ineffective.

     Tip: A servicable and easily storable vortex generator can be made by
     cutting a hole in the top of an old cigar box filled with smoke, then
     pressing sharply on the bottom of the box. This is very appropriate
     if you fill it with cigar smoke. Yecch!

Some of these questions suggest additional experiments which could be
done, and definitive answers might be obtained. Of course, there's
metric tons of physics underlying every bit of it. But can it be analyzed
with the physics of an elementary course? Can we exploit that physics for
learning and concept development, or would this just be another exercise
in tinkering?

If we critically examined such things, I think we would chose not to do
many of them. We should also ask how much of what we do in class is for
entertainment and superficial motivation and how much for education.

        -- Donald